Foundation underpinning

[lxlspeedr]

I recently had underpins installed under my foundation to stabilize it from moving. The foundation under my original structure is only 30" to the bottom of the footer. Frostline in my area is 36"... common practice is to go down to 42-48" with footings. The contractor that install the underpins thought the house was sinking due to the addition of a second story on the house, myself thought it was heiving from the frost. I remodeled and added a 12' addtion out the front of the orginal building (24'x26') and added a second story loft over the old foundation. Shouldn't the newly installed underpins have gone done below the 42" mark or further?

[MountainDon]

If 36" is the "official" frost depth then that is the minimum depth the bottom of the footer should be at. Deeper is okay, just not necessary.   

As for the addition of a second story loft, it is possible that could overburden the footing ability to carry the weight. That would be difficult to ascertain after the build unless you know the width of the footing. The soil load carrying ability also comes into play as does the design snow load. Chapter 4 of the IRC covers footing sizes for different types of residential structures. A 12"wide footing can carry a 3 story building with some soils, but nothing more than a single story with poorer soils.

[lxlspeedr]

The footing is only 12" wide and 6" deep.

[MountainDon]

The footing is only 12" wide and 6" deep.

Then it depends on soil and snow load